add deopt logging to tail call transformer

lib/6to5/transformation/file.js

@@ -328,6 +328,10 @@ File.prototype.addHelper = function (name) {
   }
 };
 
+File.prototype.logDeopt = function () {
+  // todo, (node, msg)
+};
+
 File.prototype.errorWithNode = function (node, msg, Error) {
   Error = Error || SyntaxError;
 

lib/6to5/transformation/transformers/es6/tail-call.js

@@ -1,10 +1,11 @@
 "use strict";
 
-var util = require("../../../util");
-var t    = require("../../../types");
-var map  = require("lodash/collection/map");
-var flatten = require("lodash/array/flatten");
 var reduceRight = require("lodash/collection/reduceRight");
+var messages    = require("../../../messages");
+var flatten     = require("lodash/array/flatten");
+var util        = require("../../../util");
+var map         = require("lodash/collection/map");
+var t           = require("../../../types");
 
 function returnBlock(expr) {
   return t.blockStatement([t.returnStatement(expr)]);
@@ -60,6 +61,13 @@ TailCallTransformer.prototype.getParams = function () {
   return this.params = params;
 };
 
+TailCallTransformer.prototype.hasDeopt = function () {
+  // check if the ownerId has been reassigned, if it has then it's not safe to
+  // perform optimisations
+  var ownerIdInfo = this.scope.getBindingInfo(this.ownerId.name);
+  return ownerIdInfo && !ownerIdInfo.reassigned;
+};
+
 TailCallTransformer.prototype.run = function () {
   var scope = this.scope;
   var node  = this.node;
@@ -69,16 +77,16 @@ TailCallTransformer.prototype.run = function () {
   var ownerId = this.ownerId;
   if (!ownerId) return;
 
-  // check if the ownerId has been reassigned, if it has then it's not safe to
-  // perform optimisations
-  var ownerIdInfo = this.scope.getBindingInfo(ownerId.name);
-  if (!ownerIdInfo || ownerIdInfo.reassigned) return;
-
   // traverse the function and look for tail recursion
   scope.traverse(node, firstPass, this);
 
   if (!this.hasTailRecursion) return;
 
+  if (this.hasDeopt()) {
+    this.file.logDeopt(node, messages.get("tailCallReassignmentDeopt"));
+    return;
+  }
+
   //
 
   scope.traverse(node, secondPass, this);
@@ -228,6 +236,8 @@ TailCallTransformer.prototype.subTransformCallExpression = function (node) {
 
   this.hasTailRecursion = true;
 
+  if (this.hasDeopt()) return;
+
   var body = [];
 
   if (!t.isThisExpression(thisBinding)) {